ifp Universität Stuttgart EuroSDR network on Digital Camera Calibration Report Phase I (Status Oct 26, 2004)

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1 Universität Stuttgart EuroSDR network on Digital Camera Calibration Report Phase I (Status Oct 26, 2004) Michael Cramer Institute for Photogrammetry (ifp) University of Stuttgart Geschwister-Scholl-Str. 24 D D Stuttgart / Germany ifp EuroSDR network on Digital Camera Calibration Page 0

2 Final Report Phase I EuroSDR network on Digital Camera Calibration 1 Michael Cramer Institute for Photogrammetry University of Stuttgart Geschwister-Scholl-Str. 24 D D Stuttgart / Germany WWW: INTRODUCTION...3 THE DIGITAL CAMERA CALIBRATION NETWORK...5 CAMERA CALIBRATION ASPECTS...6 Definitions...6 Laboratory calibration...7 In situ calibration...8 DIGITAL CAMERA CALIBRATION...9 DSS (Applanix)...10 DMC (ZI-Imaging)...11 Single head calibration...11 Platform calibration...13 Ultracam D (Vexcel)...14 Leica ADS Lab calibration...17 Self-calibration by bundle adjustment...17 DIMAC (Dimac Systems)...18 SUMMARY...19 REFERENCES This Phase I report is based on the paper presented at the ISPRS commission congress 2004 in Istanbul, Turkey and the publications in ZfV (4(2004)) and PE&RS (December 2004). EuroSDR network on Digital Camera Calibration Page 1

3 APPENDIX A...21 Network members (Status October 2004)...21 APPENDIX B...22 Bibliography (Status October 2004)...22 Publications on network activities...22 ADS40 (Leica Geosystems)...22 DMC (ZI-Imaging)...23 UltraCam D (Vexcel Austria)...23 Dimac (Dimac-Systems)...24 DSS (Applanix)...24 TLS (Starlabo)...24 Other sensor systems...25 Calibration (general)...25 APPENDIX C...29 DMC Calibration protocol of PAN-chromatic camera head (example)...29 DMC Calibration protocol of colour camera head (example)...32 ADS40 calibration protocol (example)...35 UltracamD calibration protocol (example, only excerpts given here)...40 EuroSDR network on Digital Camera Calibration Page 2

4 Introduction The need of a camera calibration is a fundamental requirement in the context of photogrammetric data processing. For airborne sensors this calibration is typically realized under well controlled laboratory conditions. In this case, special calibration devices are used to determine the internal camera characteristics with sufficient accuracy. Using such calibration facilities (i.e. multi-collimator or goniometer), the distortion parameters of the lens in use, are estimated based on the computed obtained discrepancies between measured coordinates or angles and their apriori known values. In addition, the focal length and principle point coordinates are chosen to minimize the absolute amount of lens distortions and to realize a symmetric distortion pattern. However, this classical technique changes with the increasing availability of new digital airborne imaging systems, mainly due to the following two aspects. First, comparing digital sensor systems from their system design concepts, there are large variations within the specific system realizations and in comparison with standard analogue cameras. These can be summarized as: Frame sensor concepts versus line scanning approaches multi-head systems versus single head sensors large image format data acquisition versus medium or even small format cameras panchromatic versus multi-spectral image data recording. Table 1 summarized these design characteristical differences with respect to the currently available commercial systems. Figure 1 shows the differences in design of multi-head digital cameras compared to each other and to the standard analogue frame sensors. All of the aforementioned differences result in different calibration approaches, which have to be defined individually for each sensor type. Additionally, due to the new parallel multi-spectral imaging capability (which is one of the major selling points for the new digital sensors), calibration should not only be restricted to geometric calibration, but should also include radiometric calibration. # System Geometry Sensor heads Image format Image recording Inertial/GPS components line frame single multi large medium synchronoutopic Syn- optional 1 ADS40 2 DMC 3 Ultracam D 4 DSS 5 DIMAC 6 HRSC-Ax 7 3-DAS-1 8 Starimager Table 1, Characteristics of modern digital airborne sensor system designs mandatory EuroSDR network on Digital Camera Calibration Page 3

5 DMC ( Z/I-Imaging 2004) Ultracam D ( Vexcel 2004) DIMAC ( Dimac Systems 2003) IGN ( IGN 2003) Figure 1, Examples of camera head designs of multi-head frame based airborne digital sensors. The second fact is mainly due to the integration of the imaging sensors with additional sensors for direct sensor trajectory determination, e.g. GPS or integrated inertial/gps modules. The combination of digital imaging sensors with direct orientation components is straightforward, since they provide very accurate information of the sensors movement and which can be used for fast generation of photogrammetric products such as ortho imagery. In the case of line scanning systems a tight integration with inertial/gps sensors is mandatory for efficient image data processing. The topic of overall system calibration is then important to discuss because calibration has to cover the whole sensor system consisting of both the imaging component and the positioning component. Therefore, the more complex, extended and more general calibration procedures are needed. In this case, the aspect of in-situ calibration gains importance, since calibration should cover the whole sensor system and not only the optical part. EuroSDR network on Digital Camera Calibration Page 4

6 The Digital Camera Calibration Network The preceding discussion defines the framework of the EuroSDR initiative on Digital Camera Calibration. On the 103 rd EuroSDR Science and Steering Committee Meetings from October 15-17, 2003 in Munich/Germany the new EuroSDR project on Digital Camera Calibration has been accepted and established officially. The goal is to derive the technical background for digital camera procedures based on scientific theory and empirical research. Legal and certification aspects are put to the background for the time being. Within a first initial meeting in September 2003 all larger digital airborne camera producers already signalized their willingness to support this EuroSDR initiative. In the meantime a network has been established by a core network group who formed this network by selecting a group from experts from around the world with different areas of complementary expertise: currently more than 30 experts from the industry, universities, research institutes, and system users. The members of the network who already have joined the network since September 2003 is given in the Appendix A. The objective of the Digital Camera Calibration project is twofold: Collection of publicly available material on digital airborne camera calibration to compile an extensive report describing the current practice and methods (Phase 1). Empirical testing with focus on the development of commonly accepted procedure(s) for airborne camera calibration and testing based on the experiences and advice of individual experts (Phase 2). As a result of Phase 1 this report has been compiled based on contributions from all project participants, which is helpful for digital camera system users to increase their knowledge of digital camera calibration aspects. Additionally, an extensive bibliography of all relevant publications on airborne camera calibration topics is (partially digital) available to all interested users (see Appendix B). The second phase focuses on the development of commonly accepted procedures for camera calibration and testing. A certain number of well-controlled test flight data sets will be provided for experimental analysis, which can be used by each network member individually. It seems to be necessary to concentrate on some of the technical aspects in a sequential order, starting with geometrical aspects and verification in a limited number of test flights by different camera producers and discussion on radiometric and image quality aspects. One aspect is the design of optimal calibration flight procedures and then to test them empirically. Another aspect is collecting a list of recommendations from the system vendors about how calibration is optimally done with their systems. It has to be mentioned that the project itself will focus on the calibration of digital airborne camera systems only. The combination of LIDAR and imaging sensors is not considered since this is a registration and no calibration problem. EuroSDR network on Digital Camera Calibration Page 5

7 Camera calibration aspects Definitions Before focussing on the topic Digital Camera Calibration by presenting the applied methods for three digital systems, the general aspects of traditional camera calibration as mentioned in the Manual of Photogrammetry (Slama 1980) are briefly cited in the following: Camera calibration is the process, whereby the geometric aspects of an individual camera are determined. It is performed in the order that the photo obtained with the camera is used to produce maps, two allow measurements, whereby ground distances or elevations can be obtained and to make orthophotos. It is possible to perform calibration to some order on any camera, but the cameras used to obtain the most accurate geometric data are specially designed for that purpose (namely high-quality lenses, usually at infinity focus). High-quality includes both well defined images and accurate positioning of the image, large aperture possible without introducing excessive distortions, special geometric features like fiducials for determining a coordinate system and for controlling the film behaviour. Calibration assumes, that the thing being calibrated is stable between calibrations. Calibrated values and their accuracy are reported in a camera calibration certificate with tables and graphs. Although most of these definitions are generally valid for all types of cameras (i.e. analogue and digital), some remarks should be given related to digital sensors: As already mentioned the multi-spectral capability is one of the major selling points for the new digital sensors, hence the calibrations should not only be restricted to the geometric aspects but to the radiometry part also. Traditional calibration only focuses on the geometry task. The photo interpretation application, which obviously is of increasing future importance, is not considered especially when thinking on the small to medium format digital sensors non dedicated for airborne use but increasingly used to obtain fast and coloured images for applications in monitoring of land use changes, disaster and risk assessment, forestry and others like real estate search and promotion or tourism. Additionally, those sensors are not specially designed for highest accuracy evaluation which directly covers the point of stability between calibrations. Finally, there is no definition or standard on how the calibrations should be documented. Since there are different techniques to perform camera calibration the Manual of Photogrammetry (Slama 1980) divides between two basic methods. Their difference is due to the fact, whether the reference values for calibration are presented in object or image space: Present an array of targets at known angles to a camera which records their images. The targets may be optical stars (simulating infinite targets) or terrain targets imaged from towers, aircraft or ground. The recorded images are measured and the data reduced from the measurements provide the elements of interior orientation. Many physical controls are necessary. EuroSDR network on Digital Camera Calibration Page 6

8 Clamp a master grid in the focal plane, measure the observed angles in object space using a visual or goniometer technique. The distortion is computed from the focal length and the difference between the image and object angles. The parameters of interior orientation are closely related to camera calibration, since a camera is signed as calibrated if the parameters of interior orientation are mathematically defined, namely: Focal length f, coordinates of principle point x p and y p, and geometric distortion characteristics of the lens system, i.e. symmetric radial distortions, asymmetric distortions caused by lens decentering. No matter of the applied method, the accuracy of camera calibration depends on the quality of known geometry of targets being viewed from the camera. This is the reason for the complex and costly equipment used for laboratory calibration methods. Laboratory calibration From classical photogrammetric point of view the component driven laboratory calibration is the standard methodology used for analogue airborne frame sensors. The results of such lab calibrations are documented in the well known calibration certificates. In order to verify the validity of calibration parameters, this calibration is repeated within certain time intervals, typically each two years. Special equipment is used, where all measurements are done in very well controlled environmental conditions. The European calibrations done for example at the Zeiss (Germany) and Leica (Switzerland) calibration facilities are based on moving collimators, so-called goniometers (Figure 2a): The camera axis is fixed, pointing horizontal or vertical and the collimator is moving around the entrance node of the lenses. The precisely known grid crosses from the illuminated master grid mounted in the focal plane of the camera are projected through the lens. These grid points are coincided with the collimator telescope and the corresponding angles in object space are measured. Besides the already mentioned calibration facilities other goniometers are available for example at DLR Berlin (Germany), Simmons Aerofilms in the UK or at FGI in Finland. In contrary to the visual goniometer technique, multi-collimators are closer to the practical conditions in photogrammetry, since the relevant information is presented in object space. A fixed array of collimators (typically arranged in a fan with well defined angles between the different viewing directions) is used, where each collimator projects an image of its individual cross hair on a photographic plate fixed in the camera focal plane (Figure 2b). The coordinates of these crosses (radial distances) are measured afterwards and from these observations the calibration parameters are obtained. In addition to the goniometer method, the multi-collimator is more efficient and the calibration includes not only the lens but the photographic emulsion on the plate fixed in the camera. Such approach finally leads to the more general system driven view considering not only one individual component during calibration (i.e. the lens of the tested camera), but including all other important components forming the overall system. EuroSDR network on Digital Camera Calibration Page 7

9 (a) Goniometer (b) Multi-collimator Figure 2, Principles of laboratory calibration (Source Bucholtz & Rüger (1973), p. 46) Although most of photogrammetric systems users feel sufficient with the traditional system component calibration, the need for overall calibration is already obvious since the 1970 as it can be seen i.e. from Maier (1978). This system calibration gains in importance, especially when including additional sensor like GPS/IMU for the data evaluation process. Typically such overall system calibrations are only possible with systems in situ approaches of calibration. In situ calibration In situ calibrations are characteristic for close range applications: Camera calibration and object reconstruction is done within one process named simultaneous calibration. Within this scenario the system and its valid parameters at the time of image recording (including all effects from the actual environment) are considered in calibration which is different from lab calibration described before. Here the camera is calibrated in the environmental conditions and at the object to be reconstructed. Typically the object reconstruction is the primary goal of this measurement campaign, hence the image block configuration might be sub-optimal for the calibration task. Within other approaches, like test site calibration or self-calibration, the calibration is of primary interest. With the use of 3D terrestrial calibration fields providing a large number of signalised points measured automatic or semi-automatic, the calibration parameters are estimated. In some cases the reference coordinates of the calibration field points are known with superior accuracy (test site calibration), although this a priori knowledge is not mandatory. Typically, the availability of one reference scale factor is sufficient (self-calibration). Since the in situ calibration is a non-aerial approach classically, appropriate mathematical calibration models are originally developed for terrestrial camera calibration. Substantial contributions in this context were given by Brown (1971, 1966), where physically interpretable and relevant parameters like focal length refinement, principal point location, radial and de-centring distortion parameters and other image deformations are introduced during system calibration. Brown clearly shows (from theoretical and practical point of view), that especially when using image blocks with strong geometry the method of bundle adjustment is a very powerful tool EuroSDR network on Digital Camera Calibration Page 8

10 to obtain significant self-calibration or additional parameter sets. Such parameter sets as proposed by Brown are implemented in commercial close-range photogrammetry packages (e.g. Fraser 1997). Besides this, calibration in standard aerial triangulation often relies on mathematical polynomial approaches as proposed e.g. by Ebner (1976) and Grün (1978). In contrary to the parameter sets resulting from physical phenomena, such mathematical driven polynomials are extending the model of bundle adjustment to reduce the residuals in image space. Since high correlation between calibration parameters and the estimated exterior orientation was already recognized by Brown, the Ebner or Grün polynomials are formulated as orthogonal to each other and with respect to the exterior orientation elements of imagery. Those correlations are especially due to the relatively weak geometry of airborne image blocks with their almost parallel viewing directions of individual camera stations and the normally relatively low percentage of terrain height undulations with respect to flying height. In standard airborne flight configurations variations in the camera interior orientation parameters cannot be estimated as far as no additional observations for the camera stations provided by GPS or imagery from different flying heights (resulting in different image scales) are available. This is of particular interest in case of GPS/inertial system calibration due to the strong correlations of GPS/inertial position and boresight alignment offsets with the exterior orientation of the imaging sensor, which is of increasing interest for digital camera systems supplemented with GPS/inertial components. Normally, the two modelling approaches (physical relevant versus mathematical polynomials) are seen in competition, nonetheless the estimation of physical significant parameters and polynomial coefficients is supplementary and both models can also be used simultaneously, as already pointed out in Brown (1976). Although most of the photogrammetric system users still feel it is sufficient to have only a traditional system component calibration, the obvious need for an overall calibration has grown over the last 30 years and continues to gain in importance, especially with the advent and use of additional integrated sensors like GPS and IMU. Against this background the need for an in-situ calibration approach increases since this offers the only possibility to calibrate complex digital sensor systems consisting of several sub-components within true physical environments. The in-situ calibration methodology, originating from the close range application field, solves for the calibration parameters within the object reconstruction process. Digital camera calibration Till now only general aspects of camera calibration are recalled and very few specifications on the calibration of digital cameras were given. Hence, some exemplarily systems already used in airborne photogrammetric applications are introduced in the following, with special focus on the applied calibration steps. Since the individual designs of digital sensor systems are quite different, only representatives of the different system classes are mentioned in the following, namely the Applanix/Emerge DSS, the ZI-Imaging DMC and the Leica ADS40 system. These sensors are representatives of the following classes: Sensor systems based on EuroSDR network on Digital Camera Calibration Page 9

11 (1) 2D matrix arrays within a single camera head (typically small to medium sized format) (2) several 2D matrix arrays combined within a multi-head solution (utilizing medium or larger format matrix arrays for each individual camera head) and finally (3) line scanning systems, where several linear CCD lines with different viewing angles and different spectral sensitivity are combined in one focal plane. The DSS is representing the systems of the first class. This group is a very vital one, since many of the already relatively low-cost semi-professional or professional digital consumer market cameras can be modified for airborne use. Petrie (2003) presents a very good overview on the 2D digital sensors market segment covering the before mentioned classes (1) and (2). The second and third group is more or less dedicated for high accuracy and large format data acquisition. The Vexcel UltracamD and the Dimac Systems DIMAC sensor are other systems which are related to class (2). Besides ADS40, other actual imaging line scanning systems being used for operational airborne photogrammetric purposes are relatively seldom. The DLR HRSC family and the Starlabo TLS scanner have to be mentioned in this context. The slightly different line scanning concept of 3-DAIS-1 was presented at the ISPRS congress by Wehrli Ass. Other imaging line scanners are used in close connection with laser scanning systems to support the automatic classification of laser points. One representative of such system integration is the Toposys Falcon laser scanner system (Toposys 2004). DSS (Applanix) The Applanix DSS is one representative of digital medium format sensor systems. The optical part is based on a MegaVision 4092 x 4077 pix CCD array digital back mounted at a Contax 645 medium format film camera housing. This housing is stabilized using a proprietary exoskeleton to maintain a more or less fixed interior camera geometry (Figure 3). The camera body itself is rigidly fixed with an Applanix POS/AV 410 GPS/inertial system, providing full exterior orientation elements for direct georeferencing. The dimension of the used CCD matrix is 3.68 x 3.67 cm² (9 x 9 m² individual pixel size) which is less compared to the size of medium format analogue films (typically between 4.5 x 6 cm² and 6 x 7 cm²). In combination with the two available lens systems of 55mm (standard) and 35mm focal length (optional) the resulting field of view is 37deg and 56deg. Comparing the field of view to the geometry of standard photogrammetric cameras (23 x 23 cm² format) these values correspond to a normal-angle (41deg, 30.5cm focal length) or medium-angle (57deg, 21.0cm focal length) image geometry, respectively. The geometric calibration of the DSS is done by terrestrial and airborne calibration. Using a calibration cage (Figure 4) imposed from different angles the interior orientation parameters of the camera are estimated, namely focal length, principle point and lens distortion parameters. In addition to the camera related parameters, the inherent misalignment between IMU body frame system and DSS camera frame is estimated. After terrestrial calibration the estimated parameters are verified from airborne data. Some more details on the applied calibration procedure, the software and the overall performance are presented in Mostafa (2004). EuroSDR network on Digital Camera Calibration Page 10

12 Figure 3, DSS medium format camera with proprietary exoskeleton for camera housing stabilization ( Applanix) Figure 4, 3D calibration cage used for terrestrial DSS camera calibration ( Applanix) DMC (ZI-Imaging) The concepts of the ZI-Imaging DMC system were firstly introduced to the photogrammetric users community during the Photogrammetric Week The official market introduction took place during the ISPRS congress 2000 in Amsterdam. This digital sensor is based on a multi-head solution using four larger format CCD frame sensors (7k x 4k pixels, pixel size 12 x 12 μm²) for the slightly tilted pan-chromatic high resolution camera heads. In Figure 1 the design of optics module is already depicted. Figure 7 shows the camera sensor unit. From the overlapping images a new image is calculated representing an perspective virtual image recorded by a large format x 7680 array. This virtual image is claimed to be free of any distortions. Hence, the knowledge of interior orientation of each individual camera head and the relative orientations between the different cameras is essential within the generation of the virtual image. The applied calibration process is divided into two steps: single head calibration and platform calibration. The approach is given in detail in Dörstel et al (2003), Zeitler et al (2002) and should be recalled here in a condensed form. The colour information is obtained from the four lower resolution colour channels applying appropriate pan-sharpening methods. Single head calibration The lab calibration of the individual camera heads is done with the goniometer measurement device available at the Zeiss Camera Calibration Centre at Oberkochen/Germany (Figures 5 and 6). This calibration unit is typically used for the calibration of analogue RMK airborne cameras. The goniometer is based on the Zeiss theodolite Th2 providing an accuracy of 1 arc sec which results in an image accuracy of 0.6 μm or 1/20 pixels assuming the nominal focal length of 12cm for the PAN camera heads. In contrary to the classical calibration, which was already before, the CCD array rigidly fixed into the camera head cannot be exchanged by a EuroSDR network on Digital Camera Calibration Page 11

13 master grid plate. This does not allow the measurement of reference points on the master grid and the correct auto-collimination of the system. Hence, the projected images of the theodolites cross-hair are measured in the digital imagery via automatic point mensuration approaches. The goniometer measurements are done in four different planes (horizontal and vertical bi-section, two diagonals), where all measurements in each plane are done twice with approx. 180deg rotated camera head. Since this rotation is slightly different from the nominal 180deg value and the auto-collimination cannot be guaranteed, additional three degrees of freedom (3 unknown rotation angles) are introduced in the subsequent calibration adjustment, which are estimated as unknown parameters for each measurement plane. These angles are describing the individual rotation between pixel- or image coordinate system of the camera head and the object coordinates realized by the goniometer for each measurement plane. Figure 5, Zeiss goniometer calibration facility ( Zeiss) Figure 6, Principle sketch of goniometer ( ZI-Imaging) The desired calibration parameters are determined via bundle adjustment, where the calibration terms are estimated as additional parameters. In order to use the bundle approach, the goniometer angle measurements are transformed into object coordinates obtained via intersection of the measured rays with a virtual plane with constant height. Within the DMC calibration the physical relevant parameter set proposed by Brown slightly modified as given by Fraser (1997) are implemented. Besides the three geometric parameters of interior orientation Δx p, Δy p and Δc, the first two (K1, K2) of the three radial symmetric parameters are always significant. In some cases the affinity and shear terms B1 and B2 are also estimated as significant. Due to the high quality lens manufacturing the tangential distortion parameters P1 and P2 are non present and eliminated typically. The accuracy ˆ σ 0 after parameter estimation is about 0.15 pixel or 1.8μm, respectively. Repeating the calibration after certain time interval shows high stability of the individual camera heads. The maximum corrections after re-calibration are documented with 1/10 of a pixel (Dörstel EuroSDR network on Digital Camera Calibration Page 12

14 et al 2003). It should be mentioned that the single head calibration parameters refer to the preliminary single head images only. Their knowledge is essential for the calculation of the virtual image but they must not been applied on the composed images when using these virtual images for photogrammetric data evaluation, which should be the standard way for DMC image data processing. The result of the camera lab calibration is documented in one calibration certificate for each camera head, respectively. Within this protocol, the estimated values of calibration parameters and their accuracy (STD) are given. Additionally, the applied distortion model formula and some general remarks are mentioned. The certificate consists of three pages. An exemplarily calibration protocol is given in Appendix C. Platform calibration The platform calibration is essential for the resampling of the new large format image composite based on the four PAN channels. Due to the fact, that a mechanical part used in high-dynamic environments like a photogrammetric flight never can be realized as absolutely stable, the DMC camera housing was designed to allow for some angular deformation of the individual camera heads relative to each other. These deformations are different for each airborne environment and have to be estimated from the mission data itself. This on-the-fly calibration approach is based on tie point measurements from the overlapping regions of pan-chromatic imagery. Besides that, the precise knowledge of relative positions of the individual camera heads, the calibration parameters from single-head calibrations as described above and first approximations on the relative misorientation between the camera heads are necessary input data required for platform calibration. The calibration is solved within a bundle adjustment approach, where three already mentioned rotation angles plus a focal length refinement for three camera heads relatively to one reference camera head are estimated As mentioned in Dörstel et al (2003) about tie points are sufficient to estimate the unknown parameters. The typically obtained accuracy is reported with 1/12 to 1/6 of a pixel. EuroSDR network on Digital Camera Calibration Page 13

15 Figure 6, DMC sensor ( ZI-Imaging) Figure 7, Ultracam D ( Vexcel) Ultracam D (Vexcel) The Ultracam D camera design is based on the use of several parallel CCD array sensor (4k x 2.7k pixels each). The sensor unit itself is given in Figure 7, where the different cones are clearly visible. Four optical cones (linearly arranged in Figure 7) are providing the high resolution pan-chromatic images, where the other 4 cones in the edges of the sensor unit are for multi-spectral data acquisition. Each panchromatic optical cone has the same field of view, but the CCD arrays are placed in different positions within each focal plane. Therefore, a stitching procedure is necessary to obtain a large format image from the different individual images. Since the pan-chromatic lenses design is based on 9 individual CCD arrays separated in the four different cones the resulting large image format is about x 7500 pixels. Within the stitching process one cone acts a master cone, to define the image coordinate system. The other images are matched as sub-images parts within this master cone frame. Since the other cones are physically displaced from the master cone, the individual image cones are triggered with certain time delays to physically realize one projection center for all 4 different pan-chromatic image cones. This new mode of image acquisition is called syntopic image recording in contrary to the more common typical synchronous data acquisition mode (each cone is triggered at the same time) used for example within the DMC sensor system. The time delay between the individual image cone triggering is dependent on the actual flying speed of the aircraft. Since the cones are physically displaced by 7cm the recording needs to be delayed by 0.001s from another, based on an aircraft speed of 70m/s. EuroSDR network on Digital Camera Calibration Page 14

16 Figure 8, Terrestrial calibration site used for UltracamD lab calibration ( Vexcel) The lab calibration part for the Vexcel Imaging Ultracam D large format digital sensor is similar to standard terrestrial close range camera test site calibrations, similar to the DSS lab calibration. A 3D terrestrial calibration field (Figure 8) with sufficient number of 240 targeted and coordinated points is recorded from three different stations with rotated and tilted camera views. Using appropriate bundle adjustment software the calibration parameters are obtained using least squares technique, where typically 84 images are taken for calibration of each individual camera head. For each cone focal length, principal point and distortions are estimated as relevant parameters. Besides that shift, scale, shear and perspective distortions are determined for each CCD. The relative orientations between the individual camera heads of Ultracam D are estimated for control purposes to detect any tilt between the different optic modules. Since the orientation between pan-chromatic master cone and the three slave camera heads is assumed to be variable, the transformation parameters are determined for each image individually from the mission site imagery itself, quite similar to the DMC approach. This is essential for stitching the individual image patches together to obtain large format imagery from the multi-head systems DMC and Ultracam D. Within this process the distortions parameters from calibration are already considered providing a (theoretically) distortion free image which is used in production then. Again, these values are verified from airborne calibration as a second step. More details on the applied calibration methods can be seen from Kröpfl et al (2004). The results of geometric individual cone calibration are listed in a quite extensive calibration sheet which is given in Appendix C. Besides that results from radiometric calibration, remarks on the lens resolving power, calibration of sensor electronics and shutter calibration are also documented in this calibration report. EuroSDR network on Digital Camera Calibration Page 15

17 Leica ADS40 In contrary to the frame based approach (single or multi-head) described so far, multiple linear CCD lines are used in the Leica ADS40 system. The ADS sensor development was driven by the experiences with digital airborne line scanning systems at DLR, namely the WAOSS/WAAC camera systems, originally designed for the 1996 Mars mission and adopted for airborne use after failure of the mission. First tests with ADS engineering models started in 1997, the official product presentation was done during the ISPRS 2000 conference in Amsterdam. The imaging part of the sensor consists of typically 10 CCD lines with different viewing angles and different multi-spectral sensitivity. Each individual line provides pix with 6.5 x 6.5 μm² pixel size. The camera sensor unit and the system aircrafts installation for an experimental flight are depicted in Figures 9 and 10. Figure 9, ADS40 sensor head ( Leica) Figure 10, ADS40 aircraft installation for experimental test flight ( Leica) During calibration the pixel positions of each individual line are determined. The nomenclature for the different CCD lines is like follows: pan-chromatic forward (PANF), nadir (PANN) and backward (PANB) lines, multi-spectral forward (red REDF, green GRNF, blue BLUF) and backward (near-infrared NIRB) lines. The viewing angle relative to the nadir looking direction is also specified by extending these identifiers with the appropriate inclusion of numbers representing the individual viewing angle. For example 28 corresponds to the 28.4deg angle between nadir and forward looking direction of the PANF channels - the resulting identifier is PANF28. The other viewing angles are 14.2deg for the backward PAN lines, 16.1deg for the RGB forward lines and 2.0deg for the NIR backward looking CCD line, resulting in 14, 16, 02 code numbers. Since each PAN channel consists of two individual lines, EuroSDR network on Digital Camera Calibration Page 16

18 shifted by half a pixel (so-called staggered arrays), this two lines are differed by using character A for the first and B for the second line. For reasons of completeness it should be mentioned, that the ADS is available with different CCD-line configurations in the focal plane also: In this case the nadir looking PAN staggered lines and the forward looking RGB lines are exchanged, resulting in nadir viewing RGB channels and an additional forward looking PAN channel. Such configuration might be advantageous, when the main focus of applications is laid on the generation of MS ortho-images. Lab calibration The lab calibration of the ADS sensor is based on a coded vertical goniometer (CVG) available at SwissOptic (a Leica Geosystems company). All details on the calibration facilities are given in Pacey et al (1999). The CVG was developed from a modified electronic vertical goniometer (EVG), where the photomultiplier is replaced by a digital CCD frame camera and the glass reference plate (with its high-precisely known marks) is replaced with a special glass code plate. These coded targets are located at the two diagonals and the two horizontal and vertical bi-sections of the plate. The spatial distance between neighbouring targets is 10mm. The measurement is done automatically with high precision. From the measured corresponding object angles the calibrated focal length and the distortion function are obtained. The CVG is used for the calibration of classical RC30 cameras as well as for the ADS sensors, although for ADS the calibration procedure has to be modified like follows. As described in Pacey et al (1999) lens cone and CCD focal plate are calibrated separately first. Afterwards both components are assembled and calibrated using the CVG. In this case the glass code plate cannot be used any longer since the CCDs are fixed in the focal plane now. Therefore, a coded target is projected in reverse direction on to the CCD-line of the tested lens. In order to allow measurements in ofnadir directions an additional mirror scanner is mounted on top of the goniometer arm. With this modification each individual pixel location on the focal plate can be addressed. As written in Schuster & Braunecker (2000) it is sufficient to measure pixels every 2-5deg within the field of view. The values for intermediate pixels are interpolated numerically. Self-calibration by bundle adjustment Although a complete measurement and process flow was established for lab calibration a new approach for ADS calibration was introduced recently. This in situ approach is exclusively based on self-calibration, which is as already mentioned before a system driven approach including the calibration of all image-relevant system components. In this context especially the inertial measurement unit (IMU) has to be mentioned, which is essential for operational processing of airborne line scanner data. The mandatory relative orientation between IMU body frame and ADS photo coordinate system can only be determined via self-calibration, which is one advantage compared to the lab calibration approach. The applied procedure is given in detail in Tempelmann et al (2003) and should be recalled in the following. The calibration is based on the orientation fixes approach proposed by Hofmann, which is implemented in the bundle adjustment software. Again the Brown parameter sets are used as calibration terms. Beside that, additional three unknowns are used to model the before mentioned misalignment angles. Although ADS40 comprises line EuroSDR network on Digital Camera Calibration Page 17

19 instead of classical frame geometry, many of the Brown parameters are directly transferable. Some of the parameters (modelling platen flatness) are not useful for line scanners and have to be eliminated. Nonetheless, some uncompensated effects remain. These remaining effects, which are non compensated via the Brown parameter set, have to be modelled by additional polynomials. In Tempelmann et al (2003) a 6 th degree of order polynomial performs sufficiently well and is recommended for X and Y components of each sensor line. This extended model will be available in the updated bundle software, hence additional polynomial coefficients are directly estimated in the bundle. In order to realize a sufficiently well overall system calibration, special requirements for the calibration flight pattern are necessary. Due to strong correlations between some of the calibration parameters and exterior orientation elements, the block layout should consist of two flight lines forming a cross, each line flown twice in bidirectional flight directions. In principle, such pattern is sufficient to estimate all parameters (even without additional ground control) except of the focal length distance. To estimate this parameter, the knowledge of a scaling factor is necessary, which can be obtained from introduction of ground control. Alternatively the same calibration block could be flown within a different flying height resulting in two different image scales. Since both blocks are connected via tie points, such block layout not only allows for calibration without any ground control but also has advantages in terms of stronger block geometry, which results in very reliable estimations of calibration parameters. Hence this double cross block layout is the recommended pattern for calibration flights. Practical tests have shown, that based on this self-calibration procedure an accuracy of μm is obtained for all ADS40 systems, which is the accuracy potential to be expected from the automatic tie point matching quality. Since the additional 6 th order polynomials are non fully integrated in the bundle adjustment (status 2003) the final self-calibration parameters are obtained from 4-6 iteration steps. It is worth to mention, that starting from the values obtained from lab calibration, only one single iteration step can be saved. From this background first trends are visible to obtain ADS40 camera calibration parameters from self-calibration exclusively. Potentially, ADS40 lab calibration will totally set away in future. The calibration results are documented in a 5 pages long calibration certificate. Within this document the tested individual system components are given and the layout of the calibration flight with tie points is depicted. The calibrated misalignment angles are given, the results of geometrical calibration (i.e. calibrated x/y coordinates of all pixels of all sensor lines) are not mentioned explicitly they are attached separately in a digital file, which belongs to the certificate. An exemplarily calibration protocol is given in Appendix C. DIMAC (Dimac Systems) The DIMAC sensor from Dimac Systems, which is a frame based sensor with a flexible combination of up to four individual camera heads, is exclusively calibrated from calibration flight data. In contrast to the DMC and Ultracam D concept, the images from the different camera heads are kept individually without merging them into a larger format virtual image during data post-processing. EuroSDR network on Digital Camera Calibration Page 18

20 Summary From the preceding discussion on the geometric calibration using different examples of modern airborne digital systems, the following statements could be summarized: System-driven calibration approaches are of increased importance in the future due to the increasing complexity of the digital sensor systems. A decreased use of classical lab calibration seems to be evident, whereas the importance of in-situ calibration (i.e. self-calibration with specific calibration flights) are definitely pursued by many vendors. The acceptance environment of a combined lab and in-situ calibration has to be increased. There are clear knowledge deficits on the users side, concerning the features and advantages of system calibration in flight. This is basically due to the fact that these are not as common in the traditional airborne photogrammetry field. With their increasing usage, such methods will be accepted as powerful and efficient tools for overall system calibration. All these aspects will be discussed in more detail and verified from experimental research in the ongoing project at hand. Generally accepted procedures for calibration shall be tested. The validation of the results will play a very important role. The technical aspects have to be treated with different priority. The geometric aspects will be treated at the beginning and shall be verified in a limited number of test flights. Various administrations and companies have offered material which will be checked by the network for best applicability in this Phase 2. Panchromatic flights shall be used for geometric resolution tests. The influence of 8-bit radiometric resolution compared to original (higher) resolution shall be evaluated with respect to the measurement accuracy. The optimal size of signals needs to be investigated for the calibration flights. The camera stability shall be checked. It has to be decided if point coordinates or derived image products (like in United States) are the optimal criteria for the evaluation, or if a combination of both would make sense. Further investigations concerning radiometric aspects, colour and general aspects of image quality are to be prepared for the second part of Phase 2. The long-term perspective of the network activities is geared towards the development of optimal calibration setup, which is appropriate for each individual sensor system design. The goal is not to compare between individual camera systems, but to distribute information to a wide range of users that can then be transferred to any new digital camera of comparable system architecture. In general, experiences within this network have already resulted in the fruitful interaction between system providers and system users. It is also expected to see more and more recommendations on system calibration and optimal data processing provided by camera manufacturers. Since camera calibration has a world-wide interest, the EuroSDR initiative has a close link with other calibration activities, mainly in the United States. With this project EuroSDR wants to support and spread this new technology in cooperation with ISPRS and experts from the US. This project thus supports also new camera vendors in the design of suitable calibration procedures. Further experts in the network are always welcome. EuroSDR network on Digital Camera Calibration Page 19

21 References Brown, D. (1966): Decentring distortions of lenses, Journal of Photogrammetric Engineerig and Remote Sensing (PE & RS), 32(3), pp Brown, D. (1971): Close range camera calibration, PE & RS, 37(8), pp Brown, D. (1976): The bundle adjustment progress and prospects, Invited paper of Com. III, XIII. ISP congress Helsinki, 33 pages. Dörstel, C., Jacobsen, K. & Stallman, D. (2003): DMC Photogrammetric accuracy calibration aspects and generation of synthetic DMC images, Proc. Optical 3D Measurements Symposium, Zurich, pp Fraser, C. (1997): Digital self-calibration, ISPRS Journal of Photogrammetry and Remote Sensing, 52(1997): Ebner, H. (1976): Self-calibrating block adjustment, Bildmessung und Luftbildwesen 44, p Grün, A. (1978): Accuracy, reliability and statistics in close-range photogrammetry, Inter-congress symposium, International Society for Photogrammetry, Com. V, Stockholm, Sweden. Meier, H.-K. (1978): The effect of environmental conditions on distortion, calibrated focal length and focus of aerial survey cameras, ISP Symposium, Tokyo. Mostafa, M. (2004): Camera/IMU boresight calibration new advances and performance analysis, accessed from 12 pages. Petrie, G. (2003): Airborne digital frame cameras, GeoInformatics 7(6), October/November 2003, pp Pacey, R.E., Scheidt, M. & Walker, S. (1999): Calibration of analog and digital airborne sensors at LH Systems, ASPRS symposium, Portland, Oregon, available on CD, 7 pages. Kröpfl, M., Kruck, E. & Gruber, M (2004): Geometric calibration of the digital large format aerial camera Ultracam D, IAPRS Volume 3, Part B, ISPRS congress, Istanbul, Turkey, available on CD, 3 pages. Schuster, R. & Braunecker, B. (2000): Calibration of the LH Systems ADS40 airborne digital sensor, IAPRS, Vol. 23, Amsterdam, digital available on CD, 7 pages. Slama, C. (1980): Manual of photogrammetry, 4 th Photogrammetry, 1056 pages. Edition, American society of Tempelmann, U., Hinsken, L. & Recke, U. (2003): ADS40 calibration and verification process, Proc. Optical 3D Measurements Symposium, Zurich, pp Toposys (2004): accessed April Zeitler, W. & Dörstel, C. (2002): Geometric calibration of the DMC: Method and results, Proc. ISPRS Com. I Symposium, Denver, available on CD, 6 pages. EuroSDR network on Digital Camera Calibration Page 20

22 Appendix A Network members (Status October 2004) # Organization Network member System providers 1 ADS 40, Leica Geosystems Mr. U. Tempelmann, Mr. P. Fricker 2 DMC, Z/I-Imaging Mr. C. Dörstel, Dr. M. Madani 3 Ultracam D, Vexcel Dr. M. Gruber 4 DIMAC, Dimac Systems Mr. P. Louis, Mr. J. Losseau 5 DSS, Applanix Corp. Dr. M. Mostafa 6 Starimager, Starlabo Corp. Dr. K. Tsuno Industry & other software developers 7 ISTAR Dr. P. Nonin 8 MacDonald Dettwiler Dr. B. Ameri 9 Vito Mr. J. Everaerts 10 Optical Metrology Centre Dr. T. Clarke 11 GIP Engineering Dr. E. Kruck 12 ORIMA Dr. L. Hinsken 13 DLR Oberpfaffenhofen Prof. M. Schroeder, Dr. P. Reinartz, Dr. R. Müller, Dr. M. Lehner University 14 Ohio State University Prof. T. Schenk, Prof. D. Merchant Prof. A. Grün, Mr. L. Zhang, Mrs. S. 15 ETH Zürich Kocaman 16 University of Glasgow Prof. G. Petrie 17 University of Rostock Dr. G. Grenzdörffer 18 University of Stuttgart Dr. N. Haala, Dr. M. Cramer 19 University of Hannover Dr. K. Jacobsen 20 Humboldt University Berlin Prof. R. Reulke 21 University of Applied Sciences Stuttgart Prof. E. Gülch 22 University of Applied Sciences Anhalt Prof. H. Ziemann 23 Institute de Geomatica Castelldefels Dr. I. Colomina 24 Agricultural University of Norway Aas Dr. I. Maalen-Johansen National mapping agencies & other authorities 25 Swedish Land Survey Mr. D. Akerman 26 Finnish Geodetic Institute Prof. R. Kuittinen, Prof. J. Hyppä 27 British Ordnance Survey Mr. P. Marshall 28 Swisstopo Landestopographie Dr. A. Streilein 29 US Geological Survey Dr. G. Stensaas, Dr. G. Y. G. Lee 30 ICC Barcelona Dr. J. Talaya 31 IGN France Dr. J. Lagrange, Dr. M. Deseilligny EuroSDR network on Digital Camera Calibration Page 21

23 Appendix B Bibliography (Status October 2004) Publications on network activities Cramer, M (2004): The EuroSDR network on digital camera calibration, in EuroSDR newsletter, No , p Cramer, M. (2004): EuroSDR network on digital camera calibration, in Proceedings ISPRS congress 2004, Istanbul, Turkey, published on CD, 6 pages. Gülch, E. & Cramer, M. (2004): Kalibrierung von digitalen Luftbildkameras, Zeitschrift für Geodäsie, Geoinformation und Landmanagement ZfV 5(2004), 129. Jahrgang, pp Cramer, M. (2004): A European network on digital camera calibration, in Photogrammetric Engineering and Remote Sensing PE&RS, to be published in December issue, ADS40 (Leica Geosystems) ADS40 calibration certificate, sample document Tempelmann, U., Hinsken, L. & Recke, U. (2003): ADS40 calibration and verification process, in Grün/Kahmen (eds.): Proceedings on Optical 3-D Measurement Techniques VI, Zürich, Switzerland, pp , also published in Proceedings International Workshop on Theory, Technology and Realities of Inertial/GPS Sensor Orientation September 2003, Castelldefels, Spain, digitally on CD-Rom. Hinsken, L., Miller, S., Tempelmann, U., Uebbing, R. & Walker, S. (2002): Triangulation of LH Systems ADS40 imagery using ORIMA GPS/IMU, IAPRS, Vol. XXXIV, Part 3A, Graz, Austria, 7 pages, digitally on CD-Rom. Schuster, R. & Braunecker, B. (2000): Calibration of the LH Systems ADS40 airborne digital sensor, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD- Rom. Tempelmann, U., Börner, A., Chaplin, B., Hinsken, L., Mykhalevych, B., Miller, S., Recke, U., Reulke, R. & Übbing, R. (2000): Photogrammetric software for the LH Systems ADS40 airborne digital sensor, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. Sandau, R., Braunecker, B., Driescher, H., Eckart, A., Hilbert, S., Hutton, J., Kirchhofer, W., Lithopoulos, E., Reulke, R. & Wicki, S. (2000): Design principles of the LH Systems ADS40 airborne digital sensor, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. Reulke, R., Franke, K.-H., Fricker, P., Pomierski, T., Sandau, R., Schönermark, M., Tornow, C., & Wiest, L. (2000): Target related multispectral and true colour EuroSDR network on Digital Camera Calibration Page 22

24 optimisation of the colour channels of the LH Systems ADS40, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. Jahn, H. & Reulke, R. (2000): Staggered line arrays in pushbroom cameras: Theory and application, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. Pacey, R.E., Walker, A.S. & Scheidt, M. (1999): Calibration of analogue and digital airborne sensors at LH Systems. Proceedings of the 1999 ASPRS Annual Conference, Portland, Oregon, pp DMC (ZI-Imaging) DMC Calibration certificate (PAN and MS Blue), sample document Dörstel, C., Jacobsen, K. & Stallmann, D. (2003): DMC Photogrammetric accuracy calibration aspects and generation of synthetic DMC images, in Grün/Kahmen (eds.): Proceedings on Optical 3-D Measurement Techniques VI, Zürich, Switzerland, pp INTERN: ifp-abschlussbericht DMC-Kamerakalibrierung, April 2001, 15 pages (excluding Appendices) Ferrano, G. & Feix, C. (2003): The Z/I-Imaging digital mapping camera system status, configuration and calibration, in Proceedings ASPRS 2003 annual conference, May 2003, Anchorage, Alaska, 5 pages, digitally on CD-Rom. Zeitler, W. & Dörstel, C. (2002): Geometric calibration of the DMC: Method and results, IAPRS, Vol. XXXIV, Part 1, Denver, Colorado, 6 pages, digitally on CD-Rom. Dörstel, C., Heier, H. & Hinz, A. (2001): System design and integration of the digital modular camera (DMC), Proceedings ASPRS 2001, St. Louis, Missouri, April 2001, 6 pages, digitally on CD-Rom. Diener, S., Kiefner, M. & Dörstel, C. (2000): Radiometric normalization and colour composite generation of the DMC, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. Hinz, A., Dörstel, C. & Heier, H. & (2000): Digital Modular Camera: System concept and data processing workflow, IAPRS, Vol. XXXIII, Part B1, Amsterdam, pp , digitally on CD-Rom. UltraCam D (Vexcel Austria) UltracamD calibration certificate (single head geometric and radiometric calibration), sample document Kröpfl, M., Kruck, E. & Gruber, M (2004): Geometric calibration of the digital large format aerial camera Ultracam D, IAPRS Volume 3, Part B, ISPRS congress, Istanbul, Turkey, available on CD, 3 pages. EuroSDR network on Digital Camera Calibration Page 23

25 Leberl, F. & Gruber, M. (2003): Flying the new large format digital aerial camera Ultracam, in Fritsch (ed.) Photogrammetric Week 2003, Wichmann Verlag, pp Leberl, F., Gruber, M., Ponticelli, Bernoegger, S. & M., Perko, R. (2003): The Ultracam large format aerial digital camera system, in Proceedings ASPRS 2003 annual conference, May 2003, Anchorage, Alaska, 7 pages, digitally on CD-Rom. Leberl, W., Perko, R., Gruber, M. & Ponticelli, M. (2002): Novel concepts for aerial digital cameras, IAPRS, Vol. XXXIV, Part 1, Denver, Colorado, 6 pages, digitally on CD-Rom. Dimac (Dimac-Systems) Information digitally available from DSS (Applanix) Mostafa, M. (2004): Airborne testing of the DSS: Test results and analysis, IAPRS Volume 3, Part B, ISPRS congress, Istanbul, Turkey, available on CD, 6 pages. Mostafa, M. (2003): Design and performance of the DSS, in Fritsch (ed.) Photogrammetric Week 2003, Wichmann Verlag, pp , also published in Proceedings International Workshop on Theory, Technology and Realities of Inertial/GPS Sensor Orientation September 2003, Castelldefels, Spain, digitally on CD-Rom. Mostafa, M. (200?): Camera/IMU boresight calibration: New advances and performance analysis, 12 pages digitally accessed from TLS (Starlabo) Poli, D. (2002): General model for airborne and spaceborne linear array sensors, IAPRS, Vol. XXXIV, Part 1, Denver, Colorado, 7 pages, digitally on CD-Rom. Grün, A. & Zhang, L (2002): Sensor modelling for aerial mobile mapping with Three- Line-Scanner (TLS) imagery, IAPRS, Vol. XXXIV, Part 2, Xian, China, pp , digitally on CD-Rom. Murai, S. & Matsumoto, Y (2000): The development of airborne three line scanner with high accuracy INS and GPS for analysing car velocity distribution, IAPRS, Vol. XXXIII, Part B2, Amsterdam, Netherlands, pp , digitally on CD-Rom. Chen, T., Shibasaki, R. & Murai, S. (2003): Development and calibration of the airborne Three-Line Scanner (TLS) imaging system, Journal of Photogrammetric Engineering and Remote Sensing, 69(1), pp EuroSDR network on Digital Camera Calibration Page 24

26 Other sensor systems Becirsphahic, F. (2003): IGN s aerial digital frame camera: From the laboratory to the production line, in Grün/Kahmen (eds.): Proceedings on Optical 3-D Measurement Techniques VI, Zürich, Switzerland, pp Lutes, J. (2002): DAIS: A digital airborne imaging system, IAPRS, Vol. XXXIV, Part 1, Denver, Colorado, 6 pages, digitally on CD-Rom. Petrie, G. (2003): Airborne digital frame cameras the technology is really improving!, Geoinformatics 6(7), Oct./Nov. 2003, pp Toth, C. (1999): Calibration experiences with integrated multisensor airborne data acquisition systems, Proceedings of the 1999 ASPRS Annual Conference, Portland, Oregon, 5 pages, digitally on CD-Rom. Calibration (general) ASPRS (2000): Camera calibration panel report, prepared by ASPRS, sponsored by USGS, January 2000, 25 pages, digitally accessible from final_report.html. Avera, H. Q. (1957): The miniature camera calibrator its design, development and use, Journal of Photogrammetric Engineering, 23(3), pp Bean, R. K. (1962): U. S. Geological Survey camera calibration, Paper, ASP-ACSM Annual convention, Washington, D.C.. Beyer, H.A. (1992): Geometric and radiometric analysis of a CCD-camera based photogrammetric close range system, Ph.D. thesis No. 9701, Institut für Geodäsie und Photogrammetrie, ETH-Hönggerberg, Mitteilungen Nr. 51, Zürich, Switzerland, 186 pages. Brown, D. (1976): The bundle adjustment progress and prospects, Invited paper of Com. III, XIII. ISP congress Helsinki, 33 pages. Brown, D. (1974): Bundle adjustment with strip- and block invariant parameters, Proceedings ISP Symposium Com. III, Stuttgart 1974, published in DGK Reihe B: Angewandte Geodäsie, Heft Nr. 214, 364 pages München Brown, D. (1971): Close range camera calibration, Journal of Photogrammetric Engineerig and Remote Sensing, 37(8), pp Brown, D. (1966): Decentring distortions of lenses, Journal of Photogrammetric Engineering and Remote Sensing, 32(3), pp Carman, P.D. (1969): Camera calibration laboratory at N.R.C., Journal of Photogrammetric Engineering, 35(4), pp Carman, P.D. & Brown, H. (1961): Camera calibration in Canada, Journal of Canadian Surveyor, 15(8), p EuroSDR network on Digital Camera Calibration Page 25

27 Carman, P.D. & Brown, H. (1956): Differences between visual and photographic calibrations of air survey cameras, Journal of Photogrammetric Engineering, 22(4), pp.??. Ebner, H. (1976): Self-calibrating block adjustment, Bildmessung und Luftbildwesen 44, p Ebner, H. (1976): Self-calibrating block adjustment, Invited paper of Com. III, XIII. ISP congress Helsinki, 17 pages. Eisenhart, C. (1963): Realistic evaluation of the precision and accuracy of instrument calibration systems, Journal of Research, National Bureau of Standards, 67c(2), April-June. Fraser, C. (1997): Digital self-calibration, ISPRS Journal of Photogrammetry and Remote Sensing, 52(1997): Gardner, I. C. (1944): The significance of the calibrated focal length, Photogrammetric Engineering, 10(1), pp. 22. Gibson, J. R. (1994): Photogrammetric calibration of a digital electro-optical stereo imaging system, GEOMATICA, Vol. 48, pp Habib, A. & Morgan, M. (2002): Automatic approach for calibrating off-the-shelf digital cameras, IAPRS, Vol. XXXIV, Part 1, Denver, Colorado, 6 pages, digitally on CD- Rom. Habib, A., Morgan, M. & Lee, Y.-R. (2002): Bundle adjustment with self-calibration using straight lines, Photogrammetric Record, 17(100), 2002, pp Hallert, B. (1955): A new method for the determination of the distortion an inner orientation of cameras and projectors, Photogrammetria, 11(3), pp Hallert, B. (1956): Some preliminary results of the determination of radial distortion in aerial pictures, Journal of Photogrammetric Engineering, 22(1), pp Hallert, B. (1962): The method of least squares applied to the multicollimator camera calibration, ASP-ACSM semiannual convention, St. Louis, Mo. Howlett, L. E. (1950): Resolution, distortion and calibration of air survey equipment, Journal of Photogrammetric Engineering, 16(1), pp Karren, R. J. (1968): Camera calibration by the multicollimator method, Journal of Photogrammetric Engineering, 34(7), pp Lewis, J (1956): A new look at lens distortion, Journal of Photogrammetric Engineering, 22(4), pp Mathieu, E. (1980): Electronic vertical goniometer: A new instrument for the geometric calibration of aerial camera lenses. Presented paper, ISP Commission I, Hamburg. Meier, H.-K. (1976): Über die geometrische Genauigkeit von Luftbildkammern, Proceedings 35 th Photogrammetric Week, published in Schriftenreihe Institut für Photogrammetrie Stuttgart, Heft 2, pp EuroSDR network on Digital Camera Calibration Page 26

28 Meier, H.-K. (1975): Über den Einfluss von Umweltbedingungen auf die Verzeichnung von Luftbildkammern, Bildmessung und Luftbildwesen BuL, 2/1975. Merchant, D. (2000): Photogrammetric resection differences based on laboratory vs. operational calibrations, IAPRS, Vol. XXXIII, Part B3, Amsterdam, pp , digitally on CD-Rom. Merchant, D. (1974): Calibration of air photo system, Photogrammetric Engineering, 40(5), pp , May Merchant, D. (1977): An analysis of aerial photogrammetric camera calibrations: A summary report, The Ohio State University Research Foundation, Geodetic science report No. 264, Columbus, Ohio. Merritt, E. L. (1950): Goniometer method of camera calibration, Report of U.S. Naval Interpretation Centre. Ohlholf, T. & Kornus, W. (1994): Geometric calibration of digital three-line CCD cameras, IAPRS, Vol. XXX, Part 1, Como, Italy, pp Roelofs, R. (1950/51): Distortion, principal point, point of symmetry and calibrated principal point, Photogrammetria, 7(2), pp Robson, S. & Shortis, M.R (1998): Practical influences of geometric and radiometric image quality provided by different digital camera systems, Photogrammetric Record, 16(92): Roos, W. (1941): Neue Definition einiger Grundbegriffe der Bildmessung, Bildmessung und Luftbildwesen 1941, Heft 16. Roos, W. (1952): Über die Definition der photogrammetrischen Grundbegriffe, A.V.N. 1952, Heft 3. Schuster, R. (1994): Sensor calibration and geometric calibration of a three line stereo camera, IAPRS, Vol. XXX, Part 1, Como, Italy, pp Shortis, M.R., Robson, S. & Beyer, H.A. (1998): Principal point behaviour and calibration parameter models for Kodak DCS cameras, Photogrammetric Record, 16(92): Tayman, W. (1974): Calibration of lenses and cameras at the USGS, Journal Photogrammetric Engineering, 40(11), pp Toth, C. (1999): Calibration experiences with integrated multi-sensor airborne data acquisition systems, Proceedings ASPRS 1999 annual conference, May 1999, Portland, Oregon, 5 pages, digitally on CD-Rom. Washer, F. E. (1957): Calibration of airplane cameras, Journal of Photogrammetric Engineering, 23(5), pp Washer, F. E. (1963): The precise evaluation of lens distortion, Journal of Photogrammetric Engineering, 29(2), pp Washer, F. E. & Case, F. A. (1950): Calibration of precision airplane camera calibration, Journal of Photogrammetric Engineering, 16(4), pp EuroSDR network on Digital Camera Calibration Page 27

29 Washer, F. E., Tayman, W. P. & Darling, W. R. (1958): Evaluation of lens distortion by visual and photographic methods, Journal of Research, National Bureau of Standards, 61(6), pp Washer, F. E., & Darling, W. R. (1959): Evaluation of lens distortion by the modified goniometric method. Journal of Research, National Bureau of Standards, 63c(2), pp EuroSDR network on Digital Camera Calibration Page 28

30 Appendix C DMC Calibration protocol of PAN-chromatic camera head (example) EuroSDR network on Digital Camera Calibration Page 29

31 EuroSDR network on Digital Camera Calibration Page 30

32 EuroSDR network on Digital Camera Calibration Page 31

33 DMC Calibration protocol of colour camera head (example) EuroSDR network on Digital Camera Calibration Page 32

34 EuroSDR network on Digital Camera Calibration Page 33

35 EuroSDR network on Digital Camera Calibration Page 34

36 ADS40 calibration protocol (example) EuroSDR network on Digital Camera Calibration Page 35

37 EuroSDR network on Digital Camera Calibration Page 36

38 EuroSDR network on Digital Camera Calibration Page 37

39 EuroSDR network on Digital Camera Calibration Page 38

40 EuroSDR network on Digital Camera Calibration Page 39

41 UltracamD calibration protocol (example, only excerpts given here) EuroSDR network on Digital Camera Calibration Page 40

42 EuroSDR network on Digital Camera Calibration Page 41

43 EuroSDR network on Digital Camera Calibration Page 42

44 EuroSDR network on Digital Camera Calibration Page 43

45 SKIPPED Calibration of pan-chromatic cones 1 3 EuroSDR network on Digital Camera Calibration Page 44